I currently have a canon 550D and am looking for a new lens and have basically norowed it down to the canon 15-85, sigma 17-50 or tamron 17-50. If anyone has used these lenses I would appreciate any feedback. I like the thought of the 15-85 but it seems to have mixed reviews. Curently I am looking for a walkabout lens for travelling.

I have a Canon 15-85mm and I think it's a great lens for the money. The IQ and sharpness are good, zoomed in or out despite the relatively wide focal range.

I'm genuinely not trying to suggest you disregard the other two lenses as both have really good ratings as well but there's no getting around the fact that that the 15-85mm has a greater range, which arguably makes it more versatile if you wish to minimise the lenses you're carrying about.

However, in the Tamron and Sigma's favour, they both have constant f/2.8 apertures so if you're in low light where it's not practical to use a low shutter speed or undesirable to bump up the ISO, they're at an advantage over the Canon in terms of how much light can get in. For portrait photography, the shallower DoF potentially puts them at an advantage as well.